USB interfaces and technically similar interfaces support what is known as “hot plugging,” that is to say the connection and removal of peripheral devices to/from a host adapter during operation of the host adapter and/or the peripheral device. At the same time, they support a multiplicity of different device types such as mice and keyboards, memory sticks, external hard disks and so on.
Particularly when external mass storage media are connected to a running computer system, however, there is the danger that the system security of a host system is put at risk. By way of example, the connection of USB memory sticks may transfer viruses or other malware to the host computer system. In addition, it is also a very simple matter to steal relatively large volumes of data.
To counteract these and similar problems, monitoring and filter mechanisms are known which prevent the connection of certain device types to a computer system.
An interface monitoring apparatus for at least one differential interface port having a positive and a negative data line D+ and D− for connecting a peripheral device is known from DE 10 2008 035 103 A1. DE '103 discloses particularly an interface monitoring apparatus that monitors an interface port based on USB specification 2.0. The circuit described therein is particularly suitable for monitoring and deactivating data lines which use continuous, differential signaling.
The USB 2.0 standard permits data transfer at a data transfer rate of no more than 480 Mbit/s. To permit data transfer at even higher data transfer rates, the subsequent USB 3.0 standard was provided with a changed physical interface port which permits data transfer at up to 5 Gbit/s. In particular, in addition to a bidirectional, differential line pair based on the USB 2.0 standard, two additional capacitively coupled, unidirectional and differential line pairs RX (Super Speed Receiver differential pair) and TX (Super Speed Transmitter differential pair) were provided which together permit bidirectional high speed communication between a USB host adapter and a USB device connected thereto. Furthermore, the USB 3.0 standard comprises further changes which relate particularly to the energy management of devices connected to a USB port.
Known interface monitoring apparatus has only limited suitability for monitoring interface ports based on the new USB 3.0 standard. The reason is that, first, the signaling used on the additional unidirectional data lines is fundamentally different than the signaling via the bidirectional data lines D+ and D− based on the USB 2.0 specification on account of the capacitive coupling of the data lines. Furthermore, the interface monitoring apparatus described in a USB 2.0 specification does not recognize the signaling via the additional differential line pairs RX and TX and, therefore, initiates unintentional deactivation of the interface port when USB 3.0 devices are connected.
It could therefore be helpful to provide an improved interface monitoring apparatus which is relatively simple design and able to ensure the intended protective effect in all cases. The interface monitoring apparatus is particularly meant to be suitable to securely and reliably monitor disconnection of devices at capacitively coupled interface ports, for example, based on USB specification 3.0.